Process for thin film deposition through controlled formation of vapor phase transient species

ABSTRACT

A method for deposition of a thin film onto a substrate is provided. The method includes providing a source precursor containing on or more of elements constituting the thin film, generating a transient species from the source precursor, and depositing a thin film onto the substrate from the transient species. The transient species being a reactive intermediate that has a limited lifetime in a condensed phase at or above room temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of co-pending U.S. patent applicationSer. No. 17/151,895, filed Jan. 19, 2021, which is a continuation ofInternational Application No. PCT/US2019/036515, filed Jun. 11, 2019,which was published on Feb. 6, 2020 under International Publication No.WO 2020/027921 A1, which claims priority to U.S. Provisional PatentApplication No. 62/713,829, filed Aug. 2, 2018 and U.S. ProvisionalPatent Application No. 62/718,424, filed Aug. 14, 2018, the disclosuresof which are herein incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

This invention relates to methods for thin film deposition includingchemical vapor deposition (CVD), atomic layer deposition (ALD), andother vapor phase deposition techniques such as molecular layerdeposition (MLD), and self-assembled monolayer (SAM) deposition thatallow the formation of a thin film onto a substrate with precisecomposition, morphology, structure, and thickness through controlledformation of vapor phase and/or surface intermediates.

The ever-increasing drive toward smaller, denser, and more functionalsemiconductor and hetero-device structures is requiring significantreduction in the thermal budget involved in the various processing stepsnecessary to grow such structures. This reduction is mandated given notonly the thermally fragile nature of the constantly decreasingthicknesses of the various thin film building blocks of such structures,but also the use of new elements in semiconductor architectures,multi-element compounds, and highly doped materials that are thermallyfragile and can lose their integrity, alter their properties andperformance, and/or react undesirably with the surroundingsubstructures. Additionally, the introduction of more flexible,typically carbon-based, substrates, such as plastic or polymersubstrates, further strains processing temperatures.

In one such critical application, chemical vapor deposition (CVD) ofepitaxial silicon (e-Si) has become an essential building block inachieving performance improvement in metal oxide semiconductor fieldeffect transistors by increasing the concentration of embedded germanium(Ge) in the Si matrix. Further strain enhancement in the embedded SiGe(e-SiGe) system is still required with decreasing feature size due todisproportionate reduction in device area caused by non-scaled gatelength. This enhancement requires lowering the CVD e-SiGe processingtemperatures below 600° C., in order to eliminate structural defects inthe deposition of silicon thin films, and employing higher orderperhydridosilanes, such as trisilane. However, trisilane was observed togenerate gas-phase particles due to much higher reactivity and lowerdissociation energy compared to silane and disilane. For example, thisconcern required lowering the partial vapor pressure of trisilane in thereaction zone during the deposition process, which again resulted in anundesirable reduction in growth rates. The deposition of n-tetrasilanewas found to provide good film quality at improved growth rates, but thelower limit of the deposition window was 650° C.

In yet another such critical application, CVD or ALD of cobalt (Co) thinand ultrathin film structures have found a myriad of new applicationsacross a variety of industrial sectors. In particular, metallic cobaltfilms play a key role in the reliability of integrated circuitry (IC)devices, as metallic cobalt films exhibit greater resistance toelectromigration and lower tendency to undergo diffusion, thereby givingthem a higher comparative stability relative to copper (Cu) inenvironments that involve both elevated temperature and high currentdensity induced stresses. These properties have compelled considerationfor a wealth of applications in IC systems, both in traditionalarchitectures as well as novel systems associated with cobalt magneticdipole moment, such as spintronic and giant magnetoresistance (GMR)devices. IC device fabrication has adopted the use of cobalt innanoscale metallization architectures.

A further advantage for IC technologies is that Co thin films can act asseed layers for electroplated cobalt and undergo post-depositionconversion to binary element compounds, such as cobalt silicide, cobaltsulfide, cobalt oxide and metallic alloys. For example, cobalt silicide(CoSi₂) conversion coatings are emerging as a viable replacement fortitanium silicide in self-aligned silicide (salicide) applications dueto a wider silicidation window, which is consistent with therequirements for generating finer line geometries. These commercialusages have spawned tremendous interest not only in optimizing andunderstanding Co film growth processes and resulting properties, butalso in expanding their use in future IC products. Other uses ofmetallic cobalt and cobalt containing films (such as oxides, sulfides,silicides and nitrides) include magneto-optic recording media, datastorage, sensor technologies, catalysts for growing carbon nanotubes andself-aligned nanowires, reflective thin films for optical devices and,more broadly, as antibacterial, decorative, protective andwear-resistant coatings.

Other critical applications include CVD and ALD of metals andsemiconductors, such as copper (Cu), ruthenium (Ru), tantalum (Ta),titanium (Ti), tungsten (W), and their nitrides, silicides, oxides andcarbides, where applicable, and CVD, ALD, MLD and SAM deposition ofdielectric, organic, and insulating films.

Accordingly, it would be highly desirable to provide a low temperatureprocess for the deposition of thin films through the controlledformation of vapor phase transient species to achieve precise filmcomposition, morphology, structure, and thickness.

BRIEF SUMMARY OF THE INVENTION

According to the invention, high quality metal, semiconductor,dielectric, diffusion barrier, adhesion and wetting layers, andinsulating films for a variety of advanced applications may be depositedor grown by CVD, ALD, MLD, or SAM deposition through the intentional andcontrolled formation of gas phase transient species that are designed toenable the growth of thin films and layered structures with specific anddesired composition, morphology, texture, and structure.

In CVD, ALD, MLD, or SAM deposition of typical unitary (single element),binary (dual element), or ternary (triple element) thin film growth, anumber of reactants comprising one or more precursors and one or morereactive or inert gases react to yield the target material. In thiscontext, a precursor is defined as a compound or complex that carriesone or more of the elements desired in the final thin film product andwhich participates in a chemical reaction to produce the ultimate targetmaterial on a substrate surface.

According to the invention, however, transient species are formed in thevapor phase from precursors and the transient species, in turn, aredirected to react with substrates at relatively low temperatures todeposit films. The formation and deposition of these transient specieson a substrate occur under conditions distinct and discrete from thetransport, deposition, or decomposition of the parent precursor. Thisdistinct and discrete generation of transient species enables thedeposition of films in lower thermal or energetic substrateenvironments, enables the deposition of films at lower temperatures andensures greater conformality of the deposited films, and allows filmdeposition on thermally or chemically fragile substrates. The transientspecies can be formed in-situ in the deposition chamber (FIG. 2), orex-situ in a synthesis chamber which is distinct from but connected tothe deposition chamber (FIG. 1).

In the context of the invention, the terms “transient” or “transitoryspecies” are intended to mean a reactive intermediate which has alimited lifetime in the condensed phase at or above room temperature andwhich is formed in the vapor phase by elimination or loss of arelatively stable or less reactive byproduct from a precursor in aninert gas stream, or in a gas that does not participate in the reaction.A transient species can also be formed by reaction of an initiallyformed transient species with another appropriate gas. The transient ortransitory species self-reaction is prevented by control of theirconcentration or their partial pressure in the vapor phase byutilization of vacuum, an inert gas or a gas that behaves as astabilizer. The invention requires that the formation of the transientspecies is well-controlled and that there is minimal generation of otherspecies that can interfere with the deposition or co-deposit with thetransient species. Implicitly, this requires that the energeticconditions needed to generate the transient species are relatively mild,with upper limits of temperature practically in a range not exceeding650° C. and electron ionization impact energies in a range not exceeding20 eV.

According to the invention, it is possible to intentionally,controllably, and purposefully create these transient species from theoriginal precursor structure and engineer their reaction, in order toeliminate undesirable gas-phase reactions or gas-phase depletionphenomena and to ensure efficient and controllable decompositionprocesses to enable the growth of thin films and layered structures withspecific and desired composition, morphology, texture, and structure.

Also, according to the invention, the transient species are engineeredsuch that the substrate surface does not drive their formation. Instead,the transient species are engineered to be more reactive with thesubstrate than their parent precursor. This is in contrast to thetraditional thermally-driven deposition of thin films, where precursorconversion to a deposited film is driven by raising the substratetemperature to afford a chemical interaction. Similarly, plasmaactivation of substrates either direct or in close-proximity to thesubstrate, contrasts with the invention, because fragile substrates arealtered or damaged by the highly energetic plasma environment.

In one embodiment, the transient species can be formed in a separatesynthesis chamber or vessel from a starting precursor, and then theseintermediates are introduced in the CVD, ALD, MLD, or SAM thin filmprocessing chamber for consumption and film formation.

In another embodiment, the transient species are produced directly inthe CVD, ALD, MLD, or SAM thin film deposition chamber.

The present invention does not include homolytic “cracking” of dimerswhich form equivalent radicals, molecular ions or radicals formed underthermal, plasma or ionizing conditions in which there are no stablebyproducts. In essence, the hemolytic cracking of dimers is inequilibrium with the starting dimers and polymers, whereas precursorsutilized in the invention lead to transient species in which thethermodynamics of deposition are intrinsically more favorable thanrecombination to form the initial precursor. By way of exemplaryexplanation, the method is entirely distinct from the concept of ex-situpyrolysis of dimeric precursor such as di-para-xylylene in a firstreaction chamber (external furnace) at very high temperatures (>680° C.)to produce a monomer such as para-xylylene, which is then released intoa second (deposition) chamber to deposit a polymeric film at roomtemperature, but can reform the dimeric precursor in or on depositedfilm. The pyrolysis reaction to form the monomer cannot be carried outin-situ in the deposition chamber, because it would interfere withchemical reaction associated with the deposition of the desired coating.

In one embodiment, high quality epitaxial silicon capable of n andp-type doping, as well as tensile and compressive strained epitaxial Si(e-Si), are prepared by utilization of the transient speciesbis(trihydridosilyl)silylene. The films can be deposited at relativelylow temperatures, namely at temperatures between 250° C. to 650° C. Forexample, bis(trihydridosilyl)silylene can be generated remotely orwithin the deposition chamber from the parent precursor isotetrasilaneby thermal decomposition or plasma-assisted conditions. The process hasadvantages associated with relatively low thermal or low energyenvironments, and also exhibits a lack of formation of siliconnanoparticles in the gas phase. Depending on processing conditions, suchas substrate temperature and transient species concentration,hydrogenated or non-hydrogenated amorphous silicon can also be formed.Alkylsilylenes can also be generated as transient species for theformation of SAMs by thermally driven hydrogen elimination hydrogen fromalkyltrihydridosilanes.

In another embodiment, pure Co films are grown from the transientspecies Co(CO)₂NO*, where the notation “*” indicates an unsatisfiedcoordination sphere. The films can be deposited at relatively lowtemperatures, namely at temperatures between 250° C. to 500° C. Forexample, Co(CO)₂NO* can be generated remotely or within the depositionchamber from the parent precursor cobalt tricarbonyl nitrosyl Co(CO)₃NOby thermal decomposition or plasma-assisted conditions. In the presenceof hydrogen, the transient species can be HCo(CO)₂NO. Similarly,HCo(CO)₃* may be a preferred transient species. The process hasadvantages associated with both relatively low thermal or low energyenvironments, and also eliminates particle formation in the gas phase.

In yet another example, the transient species Co(CO)₂* is generated byphotolysis of cobalt tricarbonyl nitrosyl at a wavelength of about220-250 nm in a carbon monoxide carrier gas. These transient species canalso be generated in a similar fashion from other cobalt carbonylcompounds, such as dicobalt octacarbonyl, dicobalt hexacarbonylt-butylacetylene and other cobalt carbonyl compounds as reviewed inKaloyeros et al, ECS Journal of Solid State Science and Technology, 8(2) P119-P152 (2019).

In another embodiment of the invention, silicon nitride films are formedby generating a transient species and then introducing the transientspecies into a deposition chamber in combination with a precursor withwhich it can then react to form a deposited film. For example, hydrogenazide is selected as a precursor since it can be intentionally andcontrollably directed at temperatures above 350° C. to form thetransient species, nitrene, (HN:), which can then be introduced into adeposition chamber in combination with trisilane depositing siliconnitride at substrate temperatures between 150° to 300° C. While thedeposition of silicon nitride at temperatures above 350° through thedirect reaction of hydrogen azide with trisilane can occursimplistically in one step rather than two steps, the substrate wouldhave to withstand temperatures above 350° C. without being thermallydamaged for the reaction to be acceptable as a single step. Theindependent formation of the nitrene reduces the potential of thermallyinduced damage to the substrate. Similarly, diazomethane can beanticipated to intentionally and controllably directed to form a carbeneby elimination of nitrogen and utilized to form silicon carbide films.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing summary, as well as the following detailed description ofthe invention, will be better understood when read in conjunction withthe appended drawings. For the purpose of illustrating the invention,there are shown in the drawings embodiments which are presentlypreferred. It should be understood, however, that the invention is notlimited to the precise arrangements and instrumentalities shown. In thedrawings:

FIG. 1 is a schematic rendering of the apparatus for ex-situ formationof transient species that are then transported to a thin film processingchamber where they react to form a thin film on a substrate;

FIG. 2 is a schematic rendering of the apparatus for in-situ formationof transient species in the thin film deposition chamber where they thenreact to form a thin film on a substrate; and

FIG. 3 is a schematic rendering of a manufacturing cluster tool equippedwith modules for ex-situ and in-situ synthesis of transient species thatare then reacted in thin film processing chambers.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to high-quality thin films formed by CVD,ALD, MLD, or SAM deposition on various substrates, and a method fordepositing such films. The method of the present invention may depositsuch films as a thin amorphous or polycrystalline film or an epitaxialfilm on a substrate.

In one embodiment, the present invention relates to silicon-rich orsilicon-based films formed from transient species generated from parentsilane precursors, and further relates to associated methods for the CVDor ALD of such films on various substrates. As used herein,“silicon-rich films” refers to epitaxial or amorphous silicon andsilicon alloys with germanium and carbon, as well as doped silicon thinfilms. For example, the silicon thin film may be doped with smallamounts of arsenic, phosphorus and boron that modify silicon'sproperties, such as conductivity.

In another embodiment, the present invention relates to cobalt-rich orcobalt-based films formed from transient species generated from parentcobalt precursors, and further relates to associated methods for the CVDor ALD of such films on various substrates. As used herein, “cobalt-richfilms” refers to epitaxial and amorphous cobalt and cobalt alloys orcompounds, such as cobalt oxide and cobalt nitride.

Such high-quality films are especially useful on substrates such assemiconductor and solar cell substrates. Examples of the substrates thatmay be utilized for formation of either silicon-rich or silicon-basedfilms or cobalt-rich or cobalt-based films include, for example, metalssuch as copper, tungsten, cobalt, ruthenium, titanium, and tantalum;metal compounds and alloys such as nitrides and carbides, silicon,silicon alloys with germanium and carbon, silicon dioxide, and the likewhich are found in IC and solar cell technologies.

There is essentially no limitation on the type of substrate that can beused in the present method. Preferably, however, the substrate isthermally and chemically stable at the conditions used for depositingthe film or films onto the substrate. That is, the substrate ispreferably stable at temperatures between about 150° C. and about 650°C. It will be understood by those skilled in the art that the thermalstability of the substrate may depend on various factors, such as thetype of film to be deposited and the intended use of the coatedsubstrate.

In the embodiment for formation of silicon-rich or silicon-based films,the parent precursors are preferably perhydridosilanes, and morepreferably perhydridosilanes having from 2 to 8 silicon atoms. Morepreferably, the parent perhydridosilane precursor for generating thetransient species to form silicon-rich or silicon-based films isisotetrasilane.

Under controlled CVD or ALD processing conditions, including specifictemperature, pressure, and key processing conditions (such as providingadditional tailored chemical, thermal, plasma, or ionization energy) tothe parent perhydridosilane precursors, the parent precursors areconverted to specific and desirable silylene transient species that aredesigned to grow epitaxial or amorphous films with specific composition,morphology and structure. For formation of the transient species,substrate temperatures are preferably in the range of 250°-600° C., andmore preferably in the range of 375-500° C. For formation of thetransient species, the reactor working pressure is preferably in therange of 10-150 torr, and more preferably in the range of 10-40 torr.

In one embodiment, the parent perhydridosilane precursor is preferablyisotetrasilane and the silylene transient species generated from theisotetrasilane is bis(trihydridosilyl)silylene ((H₃Si)₂Si), with silaneas a byproduct Bis(trihydridosilyl)silylene ((H₃Si)₂Si) can be generatedfrom isotetrasilane by a variety of methods. In particular,bis(trihydridosilyl)silylene ((H₃Si)₂Si) can be generated fromisotetrasilane under controlled processing conditions, such as direct orremote plasma-assisted conditions, electron ionization at energy levelsof 6 eV or greater (preferably between 6 eV and 15 eV, although energylevels as high as 70 eV can be employed), chemical ionization, and/orthermal decomposition at temperatures at or above 250° C.

Without wishing to be bound by theory, the mechanism for formation ofbis(trihydridosilyl)silene appears to be the controlled and reproduciblereductive elimination of silane from isotetrasilane, as shown below:

Branched perhydridosilanes, such as isotetrasilane, are preferred forthe method of the invention, because they necessarily have a relativelygreater proportion of Si atoms bonded to three hydrogens than theirlinear analogs. Branched perhydridosilanes are thus more likely toundergo dissociative adsorption. In this respect, the stickingcoefficient ε, defined as the number of adsorbed molecules per number ofimpacts, of branched perhydridosilanes is expected to be higher thanthat of their linear analogs.

As such, the invention demonstrates that isotetrasilane is a superiorcandidate for CVD e-Si, particularly relative to its lower orderperhydridosilane counterparts. The advantages of isotetrasilane include(i) the generation of bis(trihydridosilyl)silylene as the transientspecies for film formation, (ii) reduced particle formation in thereaction zone due to the inhibition of undesirable gas-phase reactions,and (iii) lower decomposition temperature due in part to its highersurface sticking coefficient.

Alternatively, bis(trihydridosilyl)silylene can be generated by thethermally-driven reaction of disilane with trisilane. Other homologs ofbis(trihydridosilyl)silylene can be generated, for example, by thereaction of disilane with n-tetrasilane.

In the embodiment for formation of cobalt-rich or cobalt-based films,the parent cobalt precursors are preferably Co⁽⁰⁾ precursors, and morepreferably Co⁽⁰⁾ precursors having a Co oxidation state of zero. In onesuch preferred embodiment, the parent Co⁽⁰⁾ precursor for generating atransient cobalt coordination complex with an unsatisfied coordinationsphere to form cobalt based films is cobalt tricarbonyl nitrosyl.

Under controlled CVD or ALD processing conditions, including specifictemperature, pressure, and key processing conditions (such as providingadditional tailored chemical, thermal, plasma, or ionization energy) tothe parent Co⁽⁰⁾ precursors, the parent cobalt precursors are convertedto specific and desirable Co(CO)₂NO* transient species that are designedto grow epitaxial or amorphous films with specific composition,morphology and structure. For formation of the transient species,substrate temperatures are preferably in the range of 100°-500° C., andmore preferably in the range of 250-400° C. For formation of thetransient species, the reactor working pressure is preferably in therange of 5-50 torr, and more preferably in the range of 5-20 torr.

In one embodiment, the parent Co⁽⁰⁾ precursor is preferably cobalttricarbonyl nitrosyl and the cobalt transient species generated from thecobalt tricarbonyl nitrosyl precursor is Co(CO)₂NO*. Co(CO)₂NO* can begenerated from cobalt tricarbonyl nitrosyl by a variety of methods,forming CO or NO as a byproduct In particular, Co(CO)₂NO* can begenerated from cobalt tricarbonyl nitrosyl under controlled processingconditions, such as direct or remote plasma-assisted conditions,electron ionization at energy levels of 1 eV or greater (preferablybetween 2 eV and 20 eV), chemical ionization, thermal decomposition,and/or photolysis. Substrate temperatures are preferably in the range of100°-500° C., and more preferably in the range of 250-400° C. Thereactor working pressure is preferably the range of 5-50 torr, and morepreferably in the range of 5-20 torr.

Without wishing to be bound by theory, the mechanism for formation ofthe preferred transient Co(CO)₂NO* appears to be the loss of CO from thecoordination sphere of cobalt in Co(CO)₃NO, as shown below:

Co(CO)₃NO→Co(CO)₂NO*+CO

The further loss of the nitrosyl group, a so-called non-innocent ligand,to form Co(CO)₂* is another preferred transient cobalt species

Referring to FIG. 2, in one embodiment, the parent precursor, and moreparticularly the parent silane or cobalt precursor, and even moreparticularly the parent perhydridosilane precursor or parent Co⁽⁰⁾precursor, is introduced into a CVD or ALD thin film deposition chamber,for production of the transient species directly in the depositionchamber, either in the vapor phase or on the substrate surface. Theparent precursors may be introduced in the deposition chamber with orwithout an inert carrier gas, such as, for example, argon, hydrogen ornitrogen. The inert carrier gas which is utilized may depend upon thetype of film to be formed. Preferably, the inert carrier gas is heliumor argon.

In such an in-situ embodiment of the method, the deposition chamber isinitially set to predetermined parameters particularly suited fortransient species generation, in order to enable the conversion of theparent precursors to the transient species within the depositionchamber.

For example, where isotetrasilane is utilized as the parent precursorand thermal decomposition is utilized to convert the isotetrasilane tothe transient silylyene species, namely bis(trihydridosilyl)silylene,the deposition chamber is preferably initially operated at a conversiontemperature between about 250° C. and about 350° C. Alternatively, wherecobalt tricarbonyl nitrosyl is utilized as the precursor and thermaldecomposition is utilized to convert the cobalt tricarbonyl nitrosyl tothe Co(CO)₂NO intermediate (i.e., transient species), the depositionchamber is preferably initially operated at a conversion temperaturebetween about 150° C. and about 250° C.

Concurrently, the substrate is preferably set to predeterminedprocessing parameters (including during substrate introduction into thedeposition reactor) to enable thermal decomposition of the transientspecies and formation of the film from the transient species (i.e.,consumption of the transient species). In the thermal depositionprocesses, the substrate is preferably operated at a depositiontemperature between about 250° C. and about 650° C., and more preferablybetween about 350° C. and about 550° C. The partial vapor pressure ofthe silylene transient species (e.g., bis(trihydridosilyl)silylene) orthe cobalt transient species (e.g., Co(CO)₂NO*) within the depositionchamber during the thermal deposition process is preferably less than 40torr. The total system processing pressure, including that of thecarrier gas and other volatile components, during the thermal depositionprocess is preferably from 1 torr up to 150 torr.

After generation of the transient species, the deposition chamber maythen optionally be purged to remove all byproducts.

In one embodiment, hydrogen is used as co-reactant, either individually,or in combination with an inert gas such as argon.

Referring to FIG. 1, in another embodiment, the parent precursor isfirst introduced into a separate synthesis chamber or vessel (i.e.,separate from the deposition chamber), where the transient species aregenerated controllably and reliably from the parent precursor, and thenthe transient species are generated and transported in the gas phase(with or without an inert carrier gas, and/or with or without aco-reactant such as hydrogen) to the CVD or ALD deposition chamber,where they are consumed in the thin film deposition process. Thetransient species may be in the deposition environment with precursormolecules and other carrier and/or reactant gases, as described above.

Preferably, the transient species synthesis chamber is connected undercontrolled conditions, such as by a vacuum interlock or valving system,to the deposition chamber. More particularly, the effluent or product ofthe transient species synthesis chamber (i.e., the silylene orCo(CO)₂NO* intermediate/transient species) is directly transported via aconduit or manifold system from the transient species synthesis chamberto the film deposition chamber. As such, the transient species synthesischamber and the deposition chamber are connected directly with eachother physically without exposure of the transient species to air or thesurrounding environment.

In some embodiments, the controlled environment under which thetransient species synthesis chamber is connected to the depositionchamber is one of vacuum, inert gas, hydrogen, reactive gas, or acombination of such gases.

In the transient species synthesis chamber, the silylene transientspecies can be generated from the perhydridosilane precursor in variousmanners, such as direct or remote plasma-assisted conditions, electronionization at energy levels of 6 eV or greater (preferably between 6 eVand 15 eV), chemical ionization, and/or thermal decomposition. In oneembodiment, where isotetrasilane is utilized as the parent precursor andthermal decomposition is utilized to convert the isotetrasilane to thesilylene transient species, particularly bis(trihydridosilyl)silylene,the transient species synthesis chamber is preferably operated at aconversion temperature between about 250° C. and about 350° C.

Similarly, in the transient species synthesis chamber, the cobalttransient species can be generated from the parent Co⁽⁰⁾ precursor invarious manners, such as direct or remote plasma-assisted conditions,electron ionization at energy levels of 1 eV or greater (preferablybetween 1 eV and 20 eV), chemical ionization, photolysis and/or thermaldecomposition. In one embodiment, where cobalt tricarbonyl nitrosyl isutilized as the parent precursor and thermal decomposition is utilizedto convert the cobalt tricarbonyl nitrosyl to the Co(CO)₂NO* transientspecies, the synthesis chamber is preferably operated at a conversiontemperature between about 150° C. and about 250° C.

In one embodiment, the transient species synthesis chamber contains amechanism for separating reaction byproducts, such as a selectiveadsorption bed (e.g., activated carbon), a molecular sieve, ametal-organic framework that removes the byproducts from the vaportransport stream, a specific chamber design, or specialized chamber flowdynamics that enable separation of byproducts from reactionintermediates.

The deposition chamber, to which the transient species are transferredfrom the synthesis chamber, is preferably operated at a depositiontemperature between about 150° C. and about 650° C., more preferablybetween about 350° C. and about 550° C. The partial processing pressureof the transient species (e.g., bis(trihydridosilyl)silylene orCo(CO)₂NO*) within the deposition chamber during thermal deposition ispreferably less than 40 torr. The total system processing pressure,including that of the carrier gas and other volatile components, ispreferably from 1 torr up to 150 torr.

With respect to the above-described embodiments, the deposition chamberis preferably equipped with a vacuum manifold and a pumping system tomaintain an appropriate pressure. It is also preferred that thedeposition chamber includes a temperature control system, and gas orvapor handling capability to meter and control the flow of reactants andproducts resulting from the process.

In all of the above-described embodiments, the deposition processtypically takes from about 30 seconds to about 30 minutes, mostpreferably about 5 minutes. However, it will be understood that the timemay vary dependent upon the type of film to be deposited, the processingconditions and the desired film thickness.

In one embodiment, under specific low temperature and low reaction vaporpressure parameters in CVD or ALD processing, and low precursor partialvapor pressure in an inert carrier gas or hydrogen stream, as discussedabove, the parent isotetrasilane is converted reliably and controllablyto the transient species bis(trihydridosilyl)silylene through thereductive elimination of silane from isotetrasilane. Thebis(trihydridosilyl)silylene has the capacity to be stable andlong-lived (i.e., half-lives consistent with transport timerequirements). Further, the bis(trihydridosilyl)silylene retains twotrihydridosilyl groups that undergo dissociative adsorption with thesubstrate, in order to produce high quality epitaxial silicon filmscapable of n and p-type doping, such as phosphorus and boron, as well astensile and compressive strained epitaxial Si (e-Si), when deposited incombination with germanium or carbon-containing precursors, germane, ortrisilapentane.

In another embodiment, the silylene transient species ispentahydrdidosilylene generated from the parent precursor n-tetrasilaneat temperatures greater than 650° C. Pentahydrdidosilylene can be useddirectly for the deposition process at temperatures below 600° C., butit also can be engineered to rearrange to bis(trihydridosilyl)silylene,a preferred transient species.

In another embodiment, bis(trihydridosilyl)silylene is formed by thereliable and reproducible reaction of disilane with trisilane attemperatures above 350° C. Without being bound by theory, the reactionis thought to occur by the decomposition of disilane to silylene(H₂Si:), hydrogen and silane. The silylene inserts into trisilaneforming isotetrasilane which, in turn, formsbis(trihydridosilyl)silylene and silane.

In one embodiment, under low temperature and low reaction vapor pressurein CVD or ALD processing, and low precursor partial vapor pressure in aninert carrier gas or hydrogen stream, as discussed above, the parentcobalt tricarbonyl nitrosyl molecule was reliably and controllablyconverted to the transient species Co(CO)₂NO* through the elimination ofCO from cobalt tricarbonyl nitrosyl. The Co(CO)₂NO* transient specieshas the capacity to be stable and long-lived (i.e., half-livesconsistent with transport time requirements). Further, the Co(CO)₂NO*retains CO and NO groups that undergo dissociative adsorption with thesubstrate, in order to produce high quality cobalt films.

The above examples of transient species are exemplary and are notintended to be limiting. Those skilled in the art recognize that othertransient species may also be formed and used in thin film depositionapplications for copper (Cu), ruthenium (Ru), tantalum (Ta), titanium(Ti), tungsten (W), and their nitrides, oxides and carbides as well asdielectric, organic, polymeric, and insulating films.

In one embodiment, as shown in FIG. 3, the inventive process may utilizea manufacturing cluster tool equipped with modules for ex-situ andin-situ synthesis of the transient species that are then reacted in thinfilm processing chambers.

The invention will now be described in terms of the following,non-limiting examples.

EXAMPLES

Example 1: The transient species bis(trihydrosilyl)silylene wasgenerated in situ by the reductive elimination of silane fromisotetrasilane. The results of these experiments are shown in Table 1.

TABLE 1 Selected Comparative Results for CVD e-Si Studies frombis(trihydridosilyl)silylene Deposition Total System Process ProcessGrowth Temperature Pressure Rate Gas Phase Example Precursor (° C.)(torr) (nm/min) Reactions 1 Silane 650° 80 11 No (comparative) 2 Silane750° 100 97 Yes. Gas (comparative) phase depletion* 3 Disilane 650° 10018 No (comparative) 4 Disilane 700° 100 28 Yes. Gas (comparative) phasedepletion* 5 n-Tetrasilane 600° 100 <10 No (comparative) 6Isotetrasilane 550° 100 13 Yes. Gas (comparative) phase depletion* 7Isotetrasilane 550° 40 26 Yes. Gas (comparative) phase depletion* 8Bis(trihydridosilyl)silylene 550° 10 35 No (innovative) 9 Isotetrasilane525° 100 18 Yes. Gas (comparative) phase depletion* 10Bis(trihydridosilyl)silylene 500° 100 12 No (innovative) *Thermodynamicpathways that lead to gas-phase depletion reactions and, ultimately,formation of particles in the gas-phase. The latter are believed to becaused by the occurrence of ring systems due to cyclization, leading tothe manifestation of gas-phase clusters (nanoparticles) which consist ofneutral or negatively charged hydrogenated silicon compounds. B. Arkleset al., Inorganic Chemistry, 2019, 58, 3050-3057.

The data shows that if the processing parameters are not tightlycontrolled, e.g., if the substrate temperature and/or parent precursorpartial pressure are too high, the parent precursor self-reacts orreacts either with other silylenes or volatile species and causes gasphase particle formation, instead of forming the desired transientspecies.

Example 2: Various experiments were conducted utilizing Co(CO)₂NO* inaccordance with the present method. The Co(CO)₂NO* was generated in situby the elimination of CO from cobalt tricarbonyl nitrosyl. The resultsof these experiments are shown in Table 2.

TABLE 2 Selected Results for CVD Co Studies from Co(CO)₂NO*. DepositionDeposition Process Process Temperature Pressure, Gas Phase Precursor (°C.) (torr) Film Composition Reactions cobalt tricarbonyl 200° 1.5 CoOcontaminated No nitrosyl with N (comparative) cobalt tricarbonyl 250°1.5 CoO contaminated No nitrosyl with N (comparative) Co(CO)₂NO* 350°1.5 Pure Co No (innovative) Co(CO)₂NO* 390° 1.5 Pure Co No (innovative)Co(CO)₂NO* 420° 1.5 Pure Co No (innovative) Co(CO)₂NO* 450° 1.5 Pure CoNo (innovative) Co(CO)₂NO* 480° 1.5 Pure Co No (innovative) *See abovenote with respect to Table 1.

The data shows a reduction in contaminants with temperature, with pureCo forming above 350° C. Significantly, if the temperature is too low,the parent precursor is partially decomposed without the formation ofthe desired intermediate, which causes film contamination.

It will be appreciated by those skilled in the art that changes could bemade to the embodiments described above without departing from the broadinventive concept thereof. It is understood, therefore, that thisinvention is not limited to the particular embodiments disclosed, but itis intended to cover modifications within the spirit and scope of thepresent invention as defined by the appended claims.

We claim:
 1. A method for deposition of a cobalt-rich thin film onto asubstrate surface, the method comprising: providing a source precursorcontaining cobalt tricarbonyl nitrosyl, generating a Co(CO)₂NO*transient species from the source precursor, wherein the transientspecies is generated independently from the substrate surface and is areactive intermediate that has a limited lifetime in a condensed phaseat or above room temperature; and subsequently depositing a thin filmonto the substrate from the transient species, wherein the film isformed independently of any chemical interaction with the substratesurface.
 2. The method of claim 1, wherein the deposition of thecobalt-rich film is carried out in a deposition chamber, a substratedeposition temperature within the deposition chamber being maintained atfrom about 100° C. to about 500° C.
 3. The method of claim 2, whereinthe substrate temperature for deposition of the cobalt-rich film ismaintained at from about 250° C. to about 400° C.
 4. The method of claim2, wherein the cobalt tricarbonyl nitrosyl is provided to the depositionchamber in a first processing step, such that the Co(CO)₂NO* isgenerated in-situ directly in the deposition chamber in the gas phase oron the surface of the substrate but independently of interaction withthe surface.
 5. The method of claim 4, wherein for generating theCo(CO)₂NO*, the deposition chamber is maintained at a temperature offrom about 150° C. to about 250° C.
 6. The method of claim 2, whereinthe cobalt tricarbonyl nitrosyl is provided to a synthesis chamber,wherein the deposition of the cobalt-rich film is carried out in adeposition chamber, the synthesis chamber being separate from andconnected to the deposition chamber under controlled conditions, andwherein the Co(CO)₂NO* is produced in the synthesis chamber from thecobalt tricarbonyl nitrosyl and is subsequently transported to thedeposition chamber for consumption and formation of the cobalt-richfilm.
 7. The method of claim 1, wherein the cobalt-rich film is anepitaxial film.
 8. The method of claim 1, wherein the cobalt-rich filmis an amorphous film.